A series of undoped or Si-doped epilayers, with a carrier concentration of between 4 x 1017 and 1.6 x 1019/cm3, were grown onto (00•1) sapphire in order to investigate the effect of Si incorporation upon stress relaxation. It was found that, as the Si doping was increased, the bound exciton peaks gradually shifted to lower energies, at the rate 0.042eV/GPa; due to the relaxation of residual thermal stresses. The results showed that the full-width at half-maximum of double-crystal X-ray diffractometry, and the intensity ratio of yellow luminescence to edge emission, increased gradually as the Si content was increased. It was proposed that the Si doping of GaN epilayers introduced widespread defects, and gave rise to stress relaxation during cooling. The yellow luminescence was attributed to a complex of VGa with the Si-induced defects.

I.H.Lee, I.H.Choi, C.R.Lee, S.K.Noh: Applied Physics Letters, 1997, 71[10], 1359-61